The present invention relates to a device for closing off the nozzle outlet area of an ink printing head forming part of an ink printing unit used in ink jet printing. The device includes an elastomer sealing cushion which, by means of a setting mechanism can be positioned with slight pressure against the nozzle outlet area.
The ink printing head, the nozzle outlet area of which is to be closed off, is filled with an aqueous ink for printing. The nozzle zone is sensitive to soiling, for example, by paper fibers and dust. Such a soiling leads to an altered nozzle geometry so that the size, shape and transfer speed of the ink droplets to be emitted from the nozzle are thereby greatly altered. A piece of lint present in front of the nozzle orifice can lead, in the suction phase of an ink printing head, such as described in German Published Accepted Patent Application (Auslegeschrift) No. 2,233,469, to an air flashback into the nozzle and thus to a failure of the system. Further, during long idle periods, there is the possibility of ink leakage out of and an air flashback into the nozzles (caused, for example, by shocks during transport) or thickening of the ink in the nozzle area.
By means of the measures described in German Laid-Open Application (Offenlegungsschrift) No. 2,754,630, contaminants can be removed by ink movement before and after the nozzle area is covered. This arrangement, however, is predicated on the discharge of the ink from the nozzles.
In German Laid-Open Application No. 2,702,663, a device is described for sealing the nozzle area of an ink printing head. For a marginal position of the ink printing head, a resiliently supported carrier is shown which has, at its freely swinging end, a mounting for a sealing cushion. The freely swinging end and the sealing cushion are, with the aid of an adjusting element, held during the printing operation of the writing unit in a position permitting the ink printing head to move into a covered position. Only thereafter is the sealing cushion placed against the nozzle exit area. The sealing cushion is an elastomer with viscous flow properties, so that even the smallest cavities in the nozzle outlet area and between the outlet area and the sealing cushion are filled up under pressure. Upon shutoff, the ink printing head must be placed into the above-noted marginal position for sealing off the nozzle outlet area.
It is known from German Laid-Open Application No. 2,742,963 to move an ink deflecting shield in front of the nozzle outlet area in any position of an ink printing head. In this arrangement, the shield is moved along with the ink printing head. However, the setting means and control means for the movement of the ink deflecting shield are also arranged on the carriage on which the ink printing head is mounted, and therefore, considerably greater moving forces are required. Moreover, the deflecting shield executes, during its movement, a wiper motion along the nozzle outlet area. Such a wiper motion in front of the nozzle area of ink printing heads of the above-outlined types can lead to their failure if thereby even the finest particles are pushed into the nozzles.